基材膜結構對滲透蒸發複合膜效能之影響

Abstract

本論文主要目的是探討無皮層基材膜之製備，包括使用蒸氣誘導式相分離(vapor induced phase inversion, VIPS)與雙凝聚劑溼式相分離結合同步塗佈(in-situ casting process)兩種鑄膜液方法製備無皮層之基材膜，也利用添加無機顆粒的方法製備表面多孔的基材膜，並進一步釐清形成無皮層基材膜的成膜機制。此外，研究中也針對無皮層基材膜所製得之複合膜運用在滲透蒸發分離上加以探討。 在PC/PAN表面多孔複合膜的製備方面，此薄膜利用VIPS結合同步塗佈兩種鑄膜液的方法所製備，可以有效得到多孔的表面結構，與傳統具有皮層之非對稱PAN薄膜相比，蒸氣誘導式相分離結合同步塗佈兩種鑄膜液所製備無皮層之PC/PAN基材膜可以有效抑制表面緻密層的生成，進而提高PC/PAN複合膜高純水透過量。在機械性質方面，隨著上層PC濃度降低而PC/PAN複合膜的機械強度會有下降的趨勢。 利用雙凝聚劑的方法製備無皮層CA (skin-free CA, SF-CA)基材膜方面，隨著CA鑄膜液在第一凝聚劑(乙醇)浸漬時間的增加，表面孔洞有變大的趨勢，且表面顆粒也趨之明顯造成表面粗糙度也隨之上升，進而提高CA基材膜的純水透過量。製備成Chitosan/ SF-CA複合膜時，運用在70oC、70 wt% IPA/H2O的滲透蒸發分離時，在維持相同的透過水濃度的情形下，以單槽成膜法為基準，此一雙凝聚劑成膜方式約可提高約50 %的純水通量。 利用同步塗佈法結合溼式相轉換法製備SF-CA基材膜方面，由於上層低濃度鑄膜液改變下層鑄膜液表面高分子濃度，造成表面高分子濃度下降，進而製得SF-CA基材膜，結果發現隨著上層CA濃度增加，其表面結構由多孔慢慢轉變成緻密的表面結構，因此造成其純水透過量與滲透蒸發透過量都有逐漸下降趨勢。數據顯示運用在滲透蒸發分離70oC 、70 wt% IPA/water時，Chitosan/SF-CA複合膜在維持相同的透過水濃度的情形下，可以提高20 %的滲透蒸發透過量。 在添加silica製備有機/無機混成薄膜(silica/PVDF)方面，結果發現純水透過量、孔洞直徑、表面孔隙度與孔洞密度隨silica添加量上升而增加，在添加7 wt%時有極大值，之後隨silica添加量上升會有下降的趨勢。將Chitosan/(silica/PVDF)複合膜，運用在70oC 、70 wt% IPA/water的滲透蒸發脫水程序，在不損失透過水濃度的情形下，添加silica之Chitosan/(silica/PVDF)複合膜比未添加之Chitosan/PVDF複合膜大約提高1000 g/m2h的滲透蒸發透過量。

The main purpose of this dissertation is to study how to prepare skin-free support membranes and to interpret the mechanism of membrane formation by the nonsolvent-induced phase separation method, which involves the absorption of water vapor to induce phase separation, combined in-situ casting process with dual coagulation or precipitation method, and added inorganic particle. Also, the effects of skin-free support membranes on their pervaporation performance were discussed. In the preparation of skin-free PC/PAN composite membranes, the membrane formation was via the vapor-induced phase separation (VIPS) method combined with in-situ casting process. This method proved effective in obtaining a porous top surface. Compared with the traditional method of preparing asymmetric PAN membrane with a dense skin layer and porous support layer, the VIPS method combined with the in-situ casting process effectively prevented skin layer formation in the ensuing PC/PAN composite membranes, resulting in the water flux increase. The mechanical properties of the PC/PAN composite membranes decreased with decreasing the PC casting layer concentration. Dual coagulation bath was the precipitation method used in forming the skin-free PC/PAN composite membranes. The surface pore size and surface roughness increased with increase in the immersion time in the first coagulation bath (ethanol), resulting in the water flux increase. Chitosan/skin-free CA composite membranes were prepared for the separation of 70 wt% IPA/H2O at 70